1. Field of the Invention
The present invention relates to corrosion inhibition and anomaly detection and, in particular, to a corrosion inhibitor which is sensitive to either neutron radiography interrogation or X-ray interrogation, and acts as a penetrant for anomaly detection.
2. Background of the Invention
Liquid/Vapor Phase Corrosion Inhibitors (LVCI) are used to mitigate or eliminate corrosion on or in non-ferrous aluminum alloys and ferrous alloy metallic structures. Such metallic structures are employed in numerous devices such as in thrust vector control (TVC) frames as part of the Space Shuttle Vehicle (SSV), solid rocket booster (SRB) system. Typically, a paint coating is applied to the surface of TVC frames.
It is advantageous to detect anomalies in the metallic structure such as anomalies due to corrosion or cracks in the metallic surface and/or joint or weld regions. Corrosion to the TVC frame may occur over multiple SRB flight use, exposure to salt air and seawater intrusion during SRB splashdown at sea, and during towback to port for refurbishment. As a result, many TVC frames have been removed from flight use because of corrosion and other surface conditions.
The conventional method to detect corrosion internal to an aluminum alloy TVC frame is through visual inspection and may include the use of a flexible borescope. Anomalous conditions such as cracks or corrosion in a substrate under a previously painted surface will not be observed. Therefore, in many cases, the extent of corrosion and anomalous welds may not be fully determined.
One problem with manual, visual inspection, including borescopic and line-of-sight inspection, is that it is extremely labor intensive. An additional problem with visual inspection is that visual inspection cannot detect corrosion and/or cracks and anomalies under the surface of previously existing coatings such as paint. In order to effectively detect the presence of an anomaly in the substrate under the painted surface, first the paint must be removed. In the case of substrates where a previously painted surface cannot effectively be removed, visual inspection is ineffective in detecting anomalies such as cracks and corrosion present in the substrate under the painted surface. A further disadvantage with borescopic inspection is that it has limited capabilities in evaluating corner areas and areas of severe bends in a metallic structure.
Due to the limitations of visual inspection, further methods have been developed specifically for detecting cracks in the metallic structure which include ultrasonic inspection and dye penetrant detection processes. While both are effective in detecting cracks, neither of these alternative detection processes are effective in detecting corrosion damage.
The anomaly detection systems developed thus far generally fail to determine the extent of corrosion or anomalous weld conditions on the surface of a substrate. Further, these previous detection methods fail to detect corrosion under a coating of paint and in structural weld regions and, in general, cannot be used to accurately inspect corner areas, interferences, and around sharp bends. In addition, the previous detection methods tend to be labor intensive, time consuming, and tedious for the inspector.
In accordance with the present invention, a dual use corrosion inhibitor and neutron ray or X-ray penetrant material allows for the rapid and accurate detection of an anomalous condition by the detection of corrosion by-products and active corrosion while also providing for the detection of discrepant welds and structural and adhesive bonded metal composite failures using a neutron ray process or X-ray process. The corrosion inhibitor acts as a penetrant material for detecting the anomalous condition during neutron radiography (N-ray) or X-ray interrogation. Specifically, the corrosion inhibitor absorbs (i.e., provides attenuation of) a N-ray or X-ray beam. Anomaly detection is provided by first applying the corrosion inhibitor sensitive to radiography interrogation on the surface of a substrate, followed by radiography interrogation. Anomalous conditions such as cracks and corrosion will appear visibly due to the attenuation of the neutron ray or X-ray beam used during radiography interrogation.
According to one aspect of the present invention, a composition is provided for application upon the surface of a substrate. The composition comprises a corrosion inhibitor sensitive to one of neutron radiography interrogation and X-ray interrogation. The corrosion inhibitor acts as a penetrant for anomaly detection on the surface of the substrate.
According to another aspect of the present invention, a system is provided for corrosion inhibition and anomaly detection. The system includes a substrate and a corrosion inhibitor applied to the substrate. The corrosion inhibitor is sensitive to either neutron radiography interrogation or X-ray interrogation and acts as a penetrate for anomaly detection on the substrate.
According to yet another aspect of the present invention, a method is provided for inhibiting corrosion and detecting an anomalous surface condition of a substrate. The method includes the steps of applying a corrosion inhibitor sensitive to either neutron radiography interrogation or X-ray interrogation and in which the corrosion inhibitor acts as a penetrant of the substrate. An anomaly is detected on the substrate using either neutron radiography or X-ray radiography.
A key feature of the present invention is a dual use material which provides both protection of a substrate by mitigating or eliminating active corrosion as well as serving as a penetrant sensitive to radiography interrogation. As a result, significant time is saved from not having to use two processes independently, namely a corrosion inhibitor process and a radiography penetrant material application process. Consequently, an advantage of the dual use material is the associated decrease in costs associated with the reduction in processing steps.
An additional feature of the present invention relates to a corrosion inhibitor sensitive to radiography interrogation which provides for the detection of currently present anomalous conditions such as cracks and corrosion, as well as for detection of future, latent structural defects or anomalies which occur in the substrate at some future point after the application of the corrosion inhibitor. For example, the present corrosion inhibitor provides for detection of anomalous conditions immediately after the application of the corrosion inhibitor to detect any initial anomalous conditions. In addition, the same substrate may be monitored for corrosion or other anomalous conditions after the substrate has been used by reexamining the substrate with radiography interrogation after the substrate has been subjected to various operating conditions and stresses.
Yet another feature of the present invention relates to the detection of anomalous surface conditions of a substrate present underneath a painted surface. The corrosion inhibitor sensitive to radiography interrogation is first applied to the surface of the substrate prior to applying a paint coating over the corrosion inhibitor. After subsequent use, the substrate can be monitored for anomalous conditions by radiography interrogation through the painted substrate surface.
One advantage of detecting an anomalous condition under a painted surface is the elimination of the need to remove the paint in order to detect the anomalous condition. Further, the present detection system provides for detecting anomalous conditions in areas where the removal of paint is difficult or impossible.
Additional features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows,